An apparatus for making bags from a multilayer synthetic-resin strip workpiece, as described in my copending patent application Ser. No. 455,919 filed Jan. 6, 1983, has a transporter for conveying the workpiece longitudinally in a transport direction along a path. A vertically displaceable upper welding element along the path has an upper upstream welding tool extending across the path, an upper downstream welding tool generally parallel thereto, and a seat extending parallel to and between the two upper tools. A blade can be fitted in the seat of the tool element to project downward from the upper tools when in the seat. Respective heatable and vertically displaceable lower upstream and downstream welding tools are vertically aligned with the upper upstream and downstream tools. A stacker pin is movable in the lower downstream tool between a position beneath same to a position projecting above same. A bottom-seaming bar is displaceable between the lower tools between a position beneath same to a position projecting above same. The machine operates for double seaming by fitting the blade in the seat, positioning the pin and bar below the lower tools and heating the respective tools with the heating means. With the machine thus set the tools are displaced from the outer to the inner positions with the workpiece between them to pinch and weld the workpiece together along upstream and downstream seams at the respective tools and to cut the workpiece across with the blade between the seams. The machine operates for bottom seaming by removing the blade from the seat and raising the pin and bar above the lower tools. When thus set the tools are displaced from the outer to the inner positions with the workpiece between them to simultaneously cut the workpiece through and form two confronting end seams with the bar while pinching it to both sides of the bar and spindling it downstream of the bar on the pin.
A similar apparatus is described in my copending application Ser. No. 455,904 filed Jan. 6, 1983. It has a transporter for conveying the workpiece longitudinally in a transport direction along a path, an upper vertically displaceable welding element along the path having relative to the direction an upper upstream welding tool extending across the path and generally parallel thereto an upper downstream welding tool, and respective vertically displaceable lower upstream and downstream welding tools vertically aligned with the upper upstream and downstream tools. A blade extends transverse to the path between one of the upstream tools and the respective downstream tool. Displacement together of the tools with a workpiece between them welds the workpiece together along upstream and downstream seams at the respective tools and cuts the workpiece across with the blade between the seams, and away from one another frees the severed downstream end section of the workpiece. A stack support downstream of the tools catches and holds the severed end sections in a stack. This stack support is displaced in the transport direction synchronously with displacement of the tools for offsetting the trailing ends of succeeding severed end sections in the stack. Thus the offset ends of the bag-forming end sections do not lie on each other so they will not fuse together.
It is possible to use such an apparatus with an output or stacking conveyor such as described in German patent document 2,003,553 filed Jan. 27, 1970 by R. Feldkamper or in U.S. Pat. No. 3,911,800 to form so-called shingled stacks of the bags. In such a stack the workpieces have lateral edges parallel to the transport direction and in vertical registration with the lateral edges of the underlying workpiece and leading and trailing edges perpendicular to the transport direction and that trail the leading and trailing edges of the underlying workpiece. This shingled arraying is advantageous when the workpieces have fresh welds that are still hot, as it keeps the welds apart so they do not fuse together.
A problem with such a conveyor, particularly when it is working with bags made of a relatively thick thermoplastic sheet, is that the workpieces shift relative to each other as they are transported. This is due to the small coefficient of sliding friction effective between the workpiece and is particularly troublesome at the upstream or intake end of the stacking conveyor where the workpieces have only partial contact with an underlying workpiece or with the conveyor surface.